Generally, there are two types of conferences:
1. Conference bridge - all sound is mixed into one stream.
2. Many-To-Many RTP streams.
I saw the first type conference for Asterisk called ConfBridge.
We tested it with audio.
I didn't hear about Asterisk video conferences though. Can you give a link to read more?
The second option, Many-To-Many RTP streams, is not supported by Flashphoner.
Also, we used and tested the following bundle: Flashphoner-(Asterisk+Diastar) Diastar is a mixing server with some control over the video conference via the IVR menu.
There's a way to solve the problem without Asteriks. the idea is, one user sends WebRTC stream, all others just play his stream back. There can be multiple users sending streams - this is called "the star". Such conference type doesn't require a mixing sever or a sip server. All streams can go via WCS.